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  1. #1

    701 blaster issues

    Apparently the 701 is reliable, but this one has been nothing but trouble for the couple of months iv'e had it. The first problem was it wouldnt maintain full revs, surge, cough and die which ended up being a split diaphragm in the carby. So i rebuilt the carb with a new rebuild kit, replaced the fuel filter and spark plugs and was running pretty good. Then yesterday it backfired whilst trying to get it to start (cold) and the waterbox exploded in half, wasnt happy, not the first time its happened either. I apoxy-welded it back together and went for another run today and it ran like crap. It revs nicely out of the water, but in the water it has no power whatsoever. I checked the reeds, theyre fine. pulled the carby completely apart, nothing wrong there. took for another run and its the same, no power and sounds doughy. could this be a fault with the ignition system? I really don't know what else i should be checking.
    Any help/ideas appreciated


  2. #2
    Yamaha artisan Cutlass's Avatar
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    maybe the backfire damaged a crank seal and now its running super lean. You could try pressure testing the engine for leaks to pinpoint it. there is a great pressure test sticky in the how-to section.

  3. #3
    mudslanger's Avatar
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    Also try running it so you can get fresh air in it. the problem might still be an exhaust leak.

  4. #4
    The waterbox seems to be sealed up good and proper, no smoke at all. thanks for mentioning that Cutlass, it didnt even occur to me that it may have bottom end damage. i just went out and did the pressure test with a cooling system pressure tester. i blocked off the intake where the carby mounts and blocked the exhaust off the the end of the riva red pipe. im not sure i have blocked everything off though, cant seem to get hardly any pressure, unless the leak is that severe..
    Im thinking it might be best to just whip the motor out and then do it so i can see whats going on, but im not sure..

  5. #5
    Yamaha artisan Cutlass's Avatar
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    sounds like you might be on the right track there.

  6. #6
    found a slight issue, the ring on the head of cyl 1 has peeled out letting the compression out into the water jacket. it appears that water has also come in through here as there is brown water residue in the cyl and crankcase. Im not sure weather to just slap new rings and gaskets in there and cross hatch the bores, or to rebuild the bottom end aswell and maybe replace pistons, head etc..

  7. #7

  8. #8
    did you just pull the head or did a compression test lead to this?

  9. #9
    yep did compression test, got 150psi on cyl 2 and about 30psi on cyl 1. This must be from that backfire.

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